ML20056H033
| ML20056H033 | |
| Person / Time | |
|---|---|
| Site: | Oconee  |
| Issue date: | 08/30/1993 |
| From: | Hampton J DUKE POWER CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| NUDOCS 9309080105 | |
| Download: ML20056H033 (3) | |
Text
1 I
, ' DukeIsucCongwy 1 Wilants
' b.
- e Oconee NudearSae Yve Ivesident i
P.0 Bax H39 (803%G3690fface Seneca, SC2.'C9 (803}&G3%4 Tax DUKEPOWER August 30, 1993 U. S. Nuclear Regulatory Commission Attention: Document Control. Desk Washington, DC 20555 Subj ect:
Oconee Nuclear Station Docket Nos. 50-269,-270,-287 Preliminary Accident Sequence Precursor Analyses By letter dated August 3,
1993, the NRC staff requested comments on the preliminary Accident Sequence Precursor (ASP) analysis regarding LER 269/92-18 (Design Deficiency Results in the Inoperability of Oconee Emergency Power Source). A summary of the review of the preliminary ASP analyses is attached.
A detailed evaluation of the subject event by Duke Power Company indicates that the event should not be classified as an accident sequence precursor.
Very Truly Yours, 7 71 6Zuto J. W.11ampton w
xc:
L. A. Viens, Project Manager ONPJL S. D. Ebneter, Regional Administrator Regicn II P. E. Ilarmon, Senior Resident It a.,.:tu r Oconee Nuclear Station 070000 9309080105 930830 PDR ADDCK 05000269 ;y, gG j
S PDR g.,
c.~ wwrm e t'.,\\
=..
i
- e. '
I i
DUKE COMMENTS ON THE PRELIMINARY ORNL/ ASP EVALUATION OF LER 269/92-018 The event described in the subj ect precursor analysis is a technical inoperability of both Keowee Hydro units at Oconee. This technical inoperability I
was the result of insufficient DC voltage which affecret the closing coils to the circuit breakers which supply the auxiliary buses and the excitation breakers at Keowee.
j Characterization of Possible Plant Response 4
The ORNL ASP evaluation makes the assumption that, due to the modification on the I
circuit breaker "X"
relays, the closing coils to Keowee auxiliary bus feeder breakers would not close the breakers automatically if required. This was not the case.
r The identified problem was an insufficient voltage to breaker closing coils which was not affected by the "X" relay modification. Both Keowee units had been black start tested before November 24, 1992 and had never experienced the problem l
identified in the LER.
1 Keowee Hydro Unit I was functionally " tested" by an actual loss of offsite power event on October 19, 1992. This event occurred after the modification to the "X" relay associated with Keowee Unit 1 (See LER 270/92-0004). During this event, both Keowee units lost auxiliary power (as expected), but recovered power on the l
first challenge when backup auxiliary bus feeder breakers closed on to the j
4 alternate source (as designed).
The field and field supply breakers also j
performed correctly during the first challenge.
j It is also noteworthy that, during the test of both Keowee units on November 24, l
1992 (described in the text of the ASP evaluation and in LER 269/92-018), the l
auxiliary t reakers for Keowee Unit 1 (and the field breakers for both Keowee d
units) did not indicate any problems. Therefore, the assumption of Keowee Unit l
1 inoperability is being made in the ASP evaluation in spite of two successful trials after the "X"
relay modification and successful trials before the 3
l modification, j
\\
For the above reasons, the period of unavailability for both Keowee Units assumed i
in the ASP evaluation (360 hours0.00417 days <br />0.1 hours <br />5.952381e-4 weeks <br />1.3698e-4 months <br />) is too large. This period should have been about 22 hours2.546296e-4 days <br />0.00611 hours <br />3.637566e-5 weeks <br />8.371e-6 months <br />.
]
I LER 269/92-18 does describe a period when both Keowee Units were functionally inoperable from December 2, 1992 at approximately 11:00 when a short circuit occurred in the control' circuit for Keowee Unit 2 to December 3, 1992 at 08:35
)
when the Keowee Unit 1-voltage regulator was repaired. This is a period of 21 hours2.430556e-4 days <br />0.00583 hours <br />3.472222e-5 weeks <br />7.9905e-6 months <br /> and 35 minutes. For most of this time, Lee Combustion turbines were being used to energize the Standby Buses at Oconee.
l i
_1_
J
4 Representation of Plant Safety Equireent The preliminary ASP evaluation says that "the use of CT-5 is described in procedures but the need for manual load shedding is not addressed," however, main feeder buses would be automatically load shed. Vital Instrumentation and Control batteries supply this function which occurs after a 20 second loss of power on I
the. main feeder buses, l'l 1
Assumptions RetardinR Recoverv Probabilities i
The backup emergency power through CT-5 (for the plant centered case) should be l
considered more reliable than assumed in this analysis. This is a simple, i
proceduralized action from the control room and it does not require a manual load shed. A value of 1.0E-03, based on operator failure to close in breakers, would I
be appropriate.
j For the ASP analysis of the October 19, 1992 loss of offsite power (LOOP) at Oconee, a value of 0.34 was assigned to failure to recover power to Keowee in the short term. Due to improvements made since that event, a lower value should now j
be tsed.
On October 28, 1992, procedure (AP/0/A/2000/002, Keowee Hydro Station - Emergency
[
Start) was implemented at Oconee. This procedure coupled with enhanced j
communication systems would make the action to restore power to the Keowee auxiliary buses more reliable.
{
l Based on the improvements since the October 19, 1992 LOOP event, a value of f
5.0E-02 for the failure to recovri Keowee power in the short term can be justified.
?
If a 22 hour2.546296e-4 days <br />0.00611 hours <br />3.637566e-5 weeks <br />8.371e-6 months <br /> exposure time and 0.2 credit for the SSF is used in the ORNL analysis, the result is a CCDF of 3.8E-07. In this case, the event is not
.j considered an accident sequence precursor.
l I
l I
i i
i i
l i
l i
i t
}
r i
'